Season the chicken breast evenly with 0.125 tsp of sea salt, 0.125 tsp of black pepper, and 0.125 tsp of dried oregano.
Heat the extra virgin olive oil in a medium stainless steel or cast iron skillet over medium-high heat until shimmering.
Place the chicken in the skillet and sear for 5 to 7 minutes per side until the exterior is golden brown and the internal temperature reaches 165 degrees Fahrenheit.
Remove the chicken from the pan and let it rest on a cutting board for 5 minutes before slicing into thin strips.
In the same skillet, add the diced yellow onion and minced garlic, sautéing for about 2 minutes until the onion is translucent and fragrant.
Add the fresh baby spinach to the skillet and toss for 1 minute until the leaves are just wilted.
Stir in the cooked jasmine rice and the sardines, using a spatula to gently break the sardines into smaller pieces while incorporating them into the rice.
Season the rice mixture with the remaining sea salt, black pepper, and dried oregano, then drizzle with lemon juice and stir to combine.
Transfer the sardine rice to a plate and top with the sliced crispy chicken breast to serve.